Here in Colorado we are fortunate to enjoy over 300 days of sunshine per year. Even in the middle of winter the sun still graces us with its warmth. So why not use this free energy to help reduce the heating demand in our homes? Passive Solar Design is a set of design principles that does just that. There are four main considerations when implementing a Passive Solar Design strategy:
- Orientation. In order to most effectively utilize the thermal gains provided by the sun’s infrared rays, we want to orient the long side of our buildings along the East-West axis. This allows for more glazing to be placed on the South While this isn’t always possible on every site, a good rule of thumb is to keep this long-axis within 20 degrees of due-south.
- Glazing Quantity and Placement. Windows can essentially be considered holes in our insulated wall system, and as such we want to prioritize placement of the windows along the south wall to allow sunlight to penetrate the space. Glazing on the east and west should be kept to less than 5% of the floor area square footage, while windows on the north should be as minimal as feasible. It is also important to specify windows with a proper heat-gain coefficient (U-value) in an effort to maximize potential benefit.
- Thermal Mass. With the building oriented correctly and windows optimally placed, we are ready to capture those rays! Infrared heat works by heating surfaces, not air. To fully take advantage of this free heat, we need to harness the sun’s energy and store it in dense materials such as concrete, masonry or an earth berm. These materials are considered ‘thermal masses’ as they absorb the infrared energy and then radiate it back out to equalize temperature Using thermal mass in floors or south-facing walls is a great application.
- Roof Overhangs and Shading. That’s right, it’s not all about thermal gains because we need to also make sure we don’t overheat a space by allowing too much sunlight We can design the roof overhang to allow the rays in during winter when the sun is lower in the sky, and keep the rays out during summer when the sun is high over-head. We use the sun’s azimuth on both the winter and summer equinoxes to determine these solar angles specific to each individual home site.
This section cut through a typical building shows these four principles in action.
So why not take advantage of this free resource to help lower our homes’ heating demand and consequently our reliance on external inputs to keep ourselves comfortable. We believe that Passive Solar Design should be incorporated in one way or another into every building we design.
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